Multipole shaking field for magnetic shielding

The authors propose a novel method of magnetic shaking for enhancing the performance of ferromagnetic shielding. The method employs a new type of planar coil which generates higher-order multipole fields. Ferromagnetic shielding walls placed close to the planar coil can be suitably shaken by its field, whereas unwanted leakage of the shaking field into the shielded space can be avoided due to the highly localized nature of the multipole field. The configuration of the novel planar coil is similar to a square mesh in which alternating cells are clockwise or counterclockwise current loops. The shaking effect on the shielding performance and the leakage of the shaking field are evaluated using cylindrical shields and compared with results obtained with toroidal shaking coils